Electric spot welding apparatus



Sept. 15, 1936. D. SCIAKY ELECTRIC SPOT WELDING APPARATUS Filed Aug. 6, 1934 6 Sheets-Sheet l Davn d. C

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6 Sheets-Sheet 2 i N VE N' z an a N I o o MN 0 H M WM- LT! ww ww W DQVIG QWMM 2; ATT V.

Sept. 15, 1936. D. SCIAKY ELECTRIC SPOT WELDING APPARATUS Filed Aug. 6, 1934 Sept 15, 1936. D. SCIAKY ELECTRIC SPOT WELDING APPARJHUS 6 Sheets-Sheet 5 Filed Aug. 6, 1954 DGVIC! sclaks IN VEN O Sept. 15, 1936. D. SCIAKY ELECTRIC SPOT WELDING APPARATUS 6 sheets-sheet 4 7 Filed Aug. 6, 1934 D f j Scic-kq P 1936- D. SCIAKY 2,054,343

ELECTRIC SPOT WELDING APPARATUS 7 Filed Aug. 6, 1934 6 Sheets-Sheet 5 By. a 18g, 10

Sept. 15, 1936. D. SCIAKY ELECTRIC SPOT WELDING APPARATUS 6 Sheets-Sheet 6 Filed Aug. 6, 1934 Patented Sept. 15, 1936 PATENT OFFICE ELECTRIC SPOT WELDING APPARATUS David Sclaky, Paris, France Application August 6, 1934, Serial No. 738,647 In France August 16, 1933 ,3 Claims. (01. 219-4) I j l d! is 01' even t: f uidt 2 t1 being the starting time of the welding, t: the

stopping time, i the intensity of the welding current and u the voltage at the terminals of the source of energy during all the time.

If only so f is measured, the power dissipated in the welding operation is a function of the intensity of 35 the current, because, the potential difference in the feeding circuit remaining constant, only the resistance of the welding can modify the intensity of the current.

In either case this measure is not exact, because the length and the form of the arms of the welding clamps as well as the presence of pieces of magnetic metal in the arms of the welding machine considerably modify the power acting for a given intensity.

It is more important to measure the energy which is developed in the welding operation by means of the voltage at the points of application of the electrodes on the metal sheets which are to be welded. 0 The method consists in measuring l: f uudt, t1

' '0 being no longer the feeding potential differ- 55 ence u, but the voltage at the points of application of the electrodes on the metal sheets to be welded.

It is known that, if the distribution which serves for feeding is alternating and sinusoidal, the above integral gives 6 This necessitates the use of the angle c corresponding to the phase shifting between the volt- 10 age and the intensity.

This method is clearly indicated in Figure 1 of the appended drawings, which shows the welding electrodes M and N, between which the voltage 0 is measured.

In practice it is very diilicult to connect the measuring winding exactly to the points of the electrodes and the above mentioned method does not on first flush appear to be commercially practicable.

The present invention consists in a method according to which the voltage 0 is replaced by a voltage 0' taken between two points P and Q which-are readily accessible (Figure 2), the wattmeter being arranged for measuring, not VI cos but a function V'I cos o) said angle (p0 corresponding to the error which has been introduced by the inactive arms of the clamps, thus permitting to substitute for the value of the voltage V the value of the voltage V, which-can be so easily measured.

The method is, therefore, characterized by the fact that the voltage is measured at points which are conveniently'spaced from the electrodes and that the various errors are corrected by determining a convenient shifting of phases between the two electric circuits which affect the measuring operation. I

The invention has to do with the above described methods irrespective of the particular 40 measuring devices used.

More particularly the invention relates to an electric spot welding installation comprising a wattmeter, having two windings, one of which is traversed bythe welding current, while to the other a voltage is applied, the phase of which is initially displaced with respect to the welding current, thus making the wattmeter easily adapted to measure whichever may be the complicated functions and the values of the variables which enter into said functions.

Assuming that the pressure at the electrodes is very high, the heat developed at the welding point remains low because, at greatintensity, the phase shift (p is also great. 'As the initial phase shift on of the current feeding the wattmeter is selectedso that rp+o is, under these conditions, nearby 90, the indication of the wattmeter remains conveniently low.

It the pressure at the electrodes diminishes, the phase shifting decreases and while the.intensity of the current is lower, more heat is conveyed to the weld. In this case +ohaving a value which difiers more than 90, the indication of the 'wattmeter is also greater.

The method of control according to the invention also takes into account the effect which is produced by the presence of magnetic pieces of metal in the neighbourhood of the conductors which supply the current. being then increased, it is necessary that the useful intensity be greater in order to deliver the same impulse to the wattmeter.

Finally, if the resistance at the welding poin is too high, either because an insulating material is inserted or because the pieces are not in contact with another, the intensity of the current will be much weaker. The indication of the wattmeter will be materially reduced, and this will represent actual conditions since the welding will be too weak inthis case. i

The indications of the wattmeter may be substantially varied by varying the value of the initial phase shift on. This control may be effected with great precision. I

Another form of execution of the invention is characterized by two wattmeters of different sendepending on the 'phase of closing and opening) the effective values of the current may be exceedingly different and consequently, welding results will be very different.

It has been proposed to-associate with the starting switch of the machine a synchronous distributor which automatically insures the closing and opening of the circuit when the sinusoidal curve attains a certain value (1. e. at a precise moment of the cycle), and which insures the closing of the contact (control pedal). For this purpose, a sector actuated, for instance, by the synchronous motor and combined with a fixed brush is usually arranged in series with the ordinary switch. The durationof the closing of the circuit is limited to the time during which the conducting sector lies under the brush. Generally this arrangement gives good results if the duration of'the closing of the circuit is very short and definitely shorter than a half-cycle. If the duration of closing of the circuit is very short, the contact of the pedal is unlikely to close when the sector lies under the brush, and the welding time is determined by the time during which the sector passes under the brush. It may happen, however, that the pedal is closed at a moment when the contact of the distributor is established,

in which case the duration is reduced and the welding will be very weak. Furthermore, it is obviously impossible to go beyond this value, that is tosay to cause the current to flow during a the aooasas considerable time, for instance during a plurality of consecutive half-cycles, since otherwise the system of getting in phase would be rendered completely illusory.

Prior investigators have assumed, therefore, that it was impossible to reconcile the problem of the multiplicity" of the half-cycles, that is to say to insure any value for the duration of the welding operation, with the well known problem or the getting in phase, that is to say of insuring the closing and the opening of the circuit .purpose a shaft with three cams driven by a synchronous motor, each of said cams closing during every revolution a contact in the relay circuits. The first relay becomes energized under the control of thefirst cam when the pedal is depressed and prepares the welding circuit, whereupon the closing of, the contact by the second cam energizes a second relay which prepares the welding circuit, the latter being closed when the second cam establishes its contact.

The closing of the contact by the third cam brings the whole device to a rest. By the above described device it is possible to close the contact of the pedal at any time. The

first cam which prepares the circuit, causes a delay whichis necessary for the shifting of the welding operation at the predetermined point on the sinusoidal curve.

The three cams coast in the following manner: the first cam prepares the circuit, the second cam closes it and maintains it closed during a plurality of consecutive half-cycles, whereby.-

greater' energy may be developed in the welding operation. The third cam brings the whole device to rest and thus prevents the execution-oi a plurality of consecutive passages of current through the same point to be welded should the pedal be maintained depressed.

It has previously been proposed to supply the anode of a rarefied gas tube containing a control grid with an alternating current and to use the phase shifting of the alternating voltage feeding the grid in order to cause the current of the anode to pass at a given point of the sinusoidal curve.

The present invention relates to a novel application of this known method to electric spot Welding machines. Thus it is possible to replace the synchronous motors and to produce one of the essential conditions for good welding with alternating current, i. e. always to close the welding circuit at a determined point of thesinusoidal curve.

' The welding machine-is equipped with an elec-' tronic valve having a biased grid to which applied an alternating current voltage which is out of phase with respect to the feeding current of the welding machine.

The welding circuit may thus be closed by means of simple static devices which are easy to adjust. for instance by means of a contactor which is fed by the valve.

These and other features of the invention will be hereinafter disclosed in greater detail and delined in the claims.

Welding machines according to the invention are shown by way of examples in drawings, in which Figs. 1 and 2 show well known circuit arrangements.

Figures 3a and 3b, which should be Joined at the line :c-y, show the diagram of a welding machine unit according to the present invention.

Figure 4 is an explanatory diagram repre-' senting the initial phase shifting of the watt.- metric current.

Figure 5 is a diagram representing the moment of closingof the welding'ci'rcuit. for switching on the current.

Figure 6 is the diagram of the control device for closing the welding circuit by means of a triode. Figure 7 is a diagram showing the operation of said device.

Figure 8 is the diagram of a third embodiment of the invention.

Figures, 9 and 10 are perspective views showing a detail of construction of said third embodiment.

Figure 11 is the diagram of another embodiment. I

Figure 12 is a perspective view of a ballistic wattmeter which may be used in the plant according to the invention. Figure 13 is a diagram of the arrangement of the circuits for the moving coil unit of said wattthe cams actuated by said motor and the relays combined with said cams.

7 in the welding operations.

(e) Group .V shows the signaling system controlled by the wattmeters and the automatic locking devices controlled by said signaling systerns.

f--Opemtion of the sunchronmis motor (Group II) in the welding plant (Group I) The sinusoidal curve S in Figure 5 shows, in the classical manner in function of time, the variations of the alternating welding current. If a is the constant welding time, the quantity of electricity which passes through the welding point is dependent on the closing point of the circuit. This point may be at b or 1), depending on which the quantities of electricity differ from another in the same way as the hatched surfaces and c'. Thus the welding circuit should always be closed at the same point of a half-cycle, if it is desired that each welding point receive the same quantity of electricity, whereby a conthe appended under the control of the device shown to the left of the transformer. Said device comprises a cam shaft I constantly revolving in the direction of the arrow I under the control of a synchronous motor I00 having a suitable demultiplicating gear ratio (Group II), thus reducing .respect to the cams; the said addusting means may be either-electrical or mechanical. For instance, it is possible electrically to operate by shifting the'alternating voltage which supplies current to the motor I00 with respect to the voltage of the supply main by known means it such as self induction coils, resistances. condensers and the like, the said means being used'alone or in combination.

The various elements constituting Group II which permit always to take the current at the same point of the sinusoidal curve operates in the following manner: V

On the cam shaft 3 are keyed three cams l, 4', 4" angularly displaced with respect to one another. The cam I prepares the relay circuits. The cam 4 then causes the welding to be effected.

' The cam 4" returns all the circuits into their initial position.

Each of the cams l, 4', 4" works on a lever B, 5" one arm of which closes a contact I, l, 1" at eachpassage of the cam risers To each contact 1, 7, 1" corresponds a relay A, B, C respectively. The three relays A, B, C

serve for the following purposes: The relay B in the operation of the machine during the cycle The above describedgeneral features may be obtained in the following manner:

The closure of the circuit of the coil 8 of A is dependent on the contact 1' of B and on a contact 9 (Group III). It is not enough that the point of the sinusoidal curve at which the current is taken be suitably selected in the known manner; provision must be made also for automatically predetermining that the sheets to be welded-have been pressed together at a suitable pressure. This is controlled by the piston ii which in turn is controlled by electromagneticvalve E of Group III, which permits the setting in operation ofthe machine, that is to say the closure of the corresponding relays only when the electrodes have been moved against one another at the required pressure.

When the pedal D of the machine'is depressed the current is conveyed to the coil of the electromagnet E, which opens the cock valve R fed through the line W; thus the pressure is established between the electrodes through the cylinas follows.

der P; the electromagnetic-valve F, which forms a true pressure-gauge, measures the pressure at the electrodes at every moment and is released when a predetermined pressure is reached and closes the contact 9. The circuit of the electromagnetic-valve E being then closed, due to the closing of the contact In, the valve admits a fluid under pressure into a cylinder H. which then tilts the member Q2. The function of this is to actue ate the contacts grouped at F. When energized, the coil 8 closes not only a contact it in the cir== cult of the primary winding of the transformer 2, but also two-other contacts i3 and it". contact it closes a line connecting a terminal of 8 with the circuit of the primary of the transformer at a terminal of the relay B. The contact l3" cooperates with the contact 7?" and the contact 9 to control the energizing circuit of the coil 8" of the relay 0.. When energized, said coil closes the contact 05 and opens the contact The first contact is in the line connecting a terminal of the coil t" with a terminal of the relay B. The second contact is in a line connecting a terminal of the coil 8" of relay B to the contact 9. when energized, coil t'closes both contacts it and it. The first contact is in series with the circuit of the coil 3 of A and with the contact l of B. The second contact is in the circuit or" the primary winding of the transformer.

In order that the unit permit a single welding only for each depression of the pedal, while the synchronous motor runs continuously, the cam 9 2 is so arranged that it is actuated in one direction only upon the. displacement of the piston it; it is thus necessary that the pressure fall again to its initial value before the circuits may be closed again and a new welding operation may be effected. The relays A, B, C, which have self-- locking contacts, can operate once only for each depression oi the pedal D.

The operation of the above described device is (a) Preparation of the circuits The machine being at rest, the electromagneticvalve and the various contacts of the same are in the position shown in the drawing. When actuated in the above explained manner, the contact 9 closes the circuit of the coil 8', so that the contacts it and it close and remain closed. If, at this moment, the cam 6 (releasing cam) closes its contact i, this produces no effect no matter 1 when the closure takes place and what its duration may be.

However, as soon as the cam 3 (preparing cam) has established the contact I, the coil 8 is energized and closes the contacts i3, i3, i8". C011 8 remains energized owing to the closure of i3 and maintains its contacts closed preparing the circuits for the welding operation. a

(11-) Welding operation' The (c) Reestablishing the. initial emission The cam t" closes the contact 1" and-therelay C opens the contact 15' and maintains it opened, whereupon the energizing. circuit or 8 is interrupted and the relay B becomes deener gized. Relay B interrupts the energizing circuit of 8 at it, and relay A also becomes deenergized. Relay A opens in contact it" the energizing circuit oi C which'becomes deenergized.

iI-Control devices The machine comprises: (a) a control device (Group IV) receiving electric current from the machine;

(b) a coupling and locking signalling device (group V) which is controlled by the control de= vice.

(a) The start or the welding current,'that is to say the exacinpoint on the sinusoidal curve where the current is taken for the welding operation, can be adjusted by moving the stator or 1 The wattmetric meters each comprise 2. voltage coil 28-25 and an intensity coil or current coil -25 which is suppliedwith current by the current transformer K. The coils operate a disc which closes contact 22-22 when rotated at a predetermined angle. The disc is then returned to normal by another coil 28 -23'.

The group H is represented by a relay I which, when its coil 26 is energized, closes both contacts 125 and 2B in circuits which are controlled by contacts closed by the member i2 when the pedal D is depressed. The closing of contact 2% holds the coil 26 energized by a circuit which can be interrupted only when a sealed button 27 is actuated. The energization of the relay I opens the contact 28 in a circuit controlled by the contact 2d, the latter being opened by the relay 1 and a contact It, which closes when the pedal.

is depressed. I

In the inactive position, i. e. when the coils 2 3 are not energized, the switches are tilted to the left in the drawings.

Case of a welding receiving insufficient energy If the welding does not receive the desired quantity of energy, none of the contacts of the wattmetric meters is closed when the welding operation is completed. A relay J which is provided with a closing dash pot and the coil of which is arranged in parallel with 8 is released at the beginning of the welding operation. At

the end of said welding operation said relay closes two contacts 8l-32 constituting safety switches, whereby the current in line i flows through the coil of relay I, which remains attracted until 21 is actuated, and which directs a current from the rectifier Ki fed by the transformer to flow in the signaling meter group H. The meter will indicate a weak welding. The lamp i8 is lighted and the acoustical signaling 19-19". The group Hi has only a single whim "lampit' and a numerical meter is.

means sounds until the button 21. is operated.

While the button 21 is'not actuated it is impos- Cacao! normal welding If the quantity of energy used in a welding operation corresponds to normal welding, the first wattmetric meter G closes its contact 22 whereupon the energizing circuit of the coil 24' of the relay 1 is closed. This relay then closes a contact 33 on a line which is open at 34 while the pedal is depressed. It moves a moving contact of the contact piece 36 onto the contact piece 31 and opens the contact 38 which served for supplying the coil I with current.

The transferof the moving contact from 36 to 31 causes current to flow through the second meter and signaling group HI, and the opening of contact 38 cuts the coil 24 of the relay I out of the circuit. The circuit of coil 24 of H! is closed by 3?, the delayed contact 35 and the contact 39 closed by the member l2. The numerical meter shows a good welding and the white lamp remains lighted until the operator re leases the pedal.

3% Case of a welding receiving too much energy When the welding receives too much energy, both wattmetric meters G-Gi close their contacts 22-42 successively. The closure of the first contact actuates the relay 1 as previously stated and before the contact 34 is closed the relay I is actuated. It closes the contact 46 through which it is held energizedaiter the opening of 22, shifts a moving,' contact from Hi to 42 and opens the contact 29.

The metering and signaling group H2 receives, therefore, current from ,the rectifier tilt. The numerical meter It shows a burnt welding and the signaling devices ill and 88" remain actu ated until the button 2'! is operated.

- In the case of weak or burnt welding the energizing current for the coils 24'-2t" is cut out at 43 when the pedal is released. The opening oi the contact 28 interrupts the circuit or the electromagneticwalve and prevents all use or the machine before the actuation of button 2'5.

During this time the feeding circuit oi the signaling devices is maintained closed by N, which closed again when the pedal is released.

Operation of the cam mechanism (Group II) When the pedal is depressed the contact It is closed. This contact causes current to flow, through the valve E (since the locked contacts 28 and 29 are closed in the position of rest). m9 Compressed air enters the cylinder P and the electrodes are brought nearer one to another and exert pressure onto the pieces to be welded.

When the small piston H serving as a pressure gauge indicates that the desired pressure is 55 attained, the contact 6 closes. I

At rest, contact I5 is closed and contact 9 when closing supplies the coil or the electromagnet i with current.

Coil 8' being supplied with current, contact I6 closes. I

Contact I. being closed, asnuell as contact 0 when contact 1' closes (under the control oi cam I) the electromagnet 8 is'supplied with current.

Atthe same time contact I. is closed. where by when contact I closes, current flows through the welding machine.

Coil 8 being supplied with current, contact l3 closes and when contact 1 is closed, switch IE is thrown out. No current flows through coil 8' and the main circuit of the welding machine is interrupted.

It is to be noted that the relays are provided with self-locking devices. For instance, if the electromagnet 8" has been supplied with current, 10 while the contact 9 of the pressure gauge remains closed, under the control of self-locking contact IS the current continuously passes through coil 8 even if contact l" is interrupted. Therefore, only a single Welding operation can be effected 15 for each actuation of the electrodes 1?.

Operation of the wattmeters The coils 2t (voltage) and it (current) co operate in causing the disc of the wattmeter to 2,0 rotate in one direction during the welding operation (the speed of rotation is a function oi the currents which pass through the coils) and thus control the machine.

Operation of the switching and indicating devices and 3% close) 535 The contact 22 of the wattrneter G on the left hand side (which indicates good weldings and too strong weldings) supplies the coil of the electro= magnet 24 with current.

The contact 22' of thewattmeter G on the 69 right hand side (which indicates only too strong weldings) supplies the coil 2%" with current.

For too weal; weldings none of the wattmeters is actuated and the contacts 22 and 22' remain open.

The relay 1 is the self-locking relay for too weak weldings.

The relay 1 is the relay for correct weldings (it represents the closure of contact E2 oi the watt'ineter G and not to the closure of contact 22 of the wattxneter G") It has no self-locking device.

The relay I is the self-locking relay for too weak weldings (which represents the simultane= ous closure of the wattmeters 22 and 22') In all these devices the positions on the left hand side is the position of rest (electromagnet without current) and the tilting to the right hand side is the operative position (electroet be ing energized).

The metering and indicating devices Hi indicate normal weldings.

The metering and indicating devices Hi. indicate excessive weldings.

If a welding is too weak the electromagnets 28' g5 and 2%" are not energized. The contact of rest 38 and the contact 3% are closed. The electromagnet 24 being energized and locked, the corn tact 28 is closed. The currentwill pass through the indicators H to: too weak weidings (it, I8, I!) as soon as the pedal is released.

Ii a welding is good, only the electromagnet 25 is energized. The switch 4| is closed by the con tact 31 and the indicators H for correct welding 35 (id' and it) will be supplied with current as soon as the pedal is released.

If a welding is too strong, then the electromagnets 2% and 24" are energized. The contacts 62 and 33 are closed and the indicators-H2 for too strong weldings will be supplied with current as soon as the pedal is released.

Embodiment according to Figure 6 In the embodiment according to Figure 6 a derivation from the main supply line I feeds the primary winding 58 of a transformer the secondary winding 'of which is divided in two sections 53'-'53". The first of the said sections feeds the heating circuit of the cathode 54 of an electronic valve 54 comprising a grid. The other is inserted in a circuit comprising a condenser 53 and a resistance 56 with a movable tap connected with the grid 54" of the said valve. The biasing voltage of the said grid has the same frequency as the feeding current, but the phase is shifted.

The anode 54" of the valve is connected with a conductor of line 8 through the switch 60 actuated by. the starting pedalof the machine. It is also connected with the movable part 51 of a relay the coil 51 of which is connected with one of the conductors of the main line and through 51' with the anode circuit of the valve while the winding is not energized.

The member 51' carries with it two similar members 58 and 59. The first of these members is inserted in a circuit which is controlled by of the main relay of the. welding machine, said coils being mounted in parallel with one another. It closes said derivation only when 51' releases.

The main relay of the welding machine has two movable contact members 52 and 63'. The first one opens the circuit of 63 when 82 is energized. The second one closes, when 83 is energized; the

circuit 64 which supplies current to the primary winding 52 of the transformer oi the welding machine. The movement of the member 62' is slowed down and the interruption takes place only after. a controllable delay which is sufllcient for the operation of the member 63'.

Owing to the provision 'of valve 54, the device always operates 'at the same point of ahalf-cycle of the current for the welding-machine as shown in Figure 7. V I

In this figure the sinusoidal curve 8 represents the feeding current for the welding machine and the sinusoidal curve B representsthe alternating potential of the grid of the ionic valve. Owing to the alternating character and to the phase shifting of said potential with respect to'the feeding current, the cathode-anode current of the valve passes only during the-fraction to of the positive half-cycles of the feeding current. The phase shifting of S with respect to S is so selected that the value of tho anode current of the valve is a .just equal, at t, to the value which is necessary for operating the relay 51-51. I

Therefore, when the operator actuates the starting device of the machine and closes the I ing' at this moment closes the members 58 and 59 its mechanically connected therewith. The member "maintains the coil 51 energized and the mem- .and the contact hl-'-h8 aosasss ber 59,-closesthe circuit of coil 82. The member e2 releases with a characteristic delay of said member while the member 63 establishes the circuit of the welding machine at the desired point .of the half-cycle and interrupts it after the time fixed by the main relay.

Embodiment according to Figure 8 This form of execution is characterized in that the closure of the main contactor of the weldin machine is dependent on a relay which is 'continuously supplied with current while the machine is inactive through the starting pedal, and

which is associated with a contact controlled by the synchronous motor so that the relay maintains I its coil energized if the contact is closed when the pedal is depressed. The coil of the contactor will be energized only when the said contact is first opened and then closed. r

In Figure 8, al is the primary winding with multiple taps of the welding machine, a2 being the secondary, winding of said transformer which feeds the contact electrodes. The primary winding ai is supplied with current under the control of the main contactor b and of the switch c. One of the terminals of said primary winding is connected with a brush at which makes contact with the edge of a disc d which is partly conductive and is rotated by a synchronous motor it. On the same edge surface rests another brush 112 which is connected with the movable armature el of a relay the coil of which is designated by e.

When the coil e is energized its contact el 1 moves against e2 which is connected with one terminal of the coil e. When said coil is not energized, el comes into contact with e3, which is connected with the control coil biof the main contactor, coil bl being connected with a return line.

The starting pedal ,1 for the welding machine is connected with one of the feeding conductors. At rest it contacts with it which is connected with coil e. When this pedal is depressed it comes against it whichis connected with the coil 9 of an auxiliary relay having two armatures which are rigidly connected with one another. Armature gl is connected with a terminal of the coil o..-

It cooperates with 92 which is connected with a return line. The ,other armature 93 cooperates with hl and 11.2, respectively, which cooperate with the movable contacts 713, M rigidly c'on-' nected with the main contactor b. The contact h2--M is closed when the contactor b is open,-'

is closed when the contactorbisclosed. Y Operation.-

when the pedal f is depressed, the circuit nor mally feeding the coil e is interrupted at H.

Two casesare then possible depending whether orv not-the brushes dland d2 are connected together at this moment by a conducting portion of disc d. If the brushes are not connected together, the

relay a being no longer energized, its movable contact el is at e3. As soon as the brushes dl and d2 are interconnected, the main contactor b tac'tor open until said connection is opened. At

this moment the movable contact el comes againstc2 and as soon as the brushes di and d2 are again connected, the current passes through hi and the main contactor closes and remains closed so long as the brushes di and d2 are connected through d.

In both cases the contactor b closes at the same point of a half-cycle and remains closed for the same time, this time depending on the angular distance between the brushes dl d2.

when closing, the contactor b interrupts the contact between h! and M and at the same time closes the contact between hi and 11.8. The coil 0 is then fed through hl, b3, 12 and f and the contact is established between gl, 9! and 93, a l. From this moment the coil 9 is again supplied with current through cl, therefore, energized when the contactor b opens at the end of the welding operation and when the contact'is broken between hi and ht. The contactor b, when opening, re-establishes the contact between at and ht. e is, therefore, also supplied with current and thecircuit of the coil bi of the\ contactor h is interrupted at ed. The coil can be no longer re-energized while the pedal is depressed. When the pedal is released the circuit continuously feeding e is rte-established at It At the same time the circuit of g is broken at 12 and causes the contacts to open at 92 and g6. Thus the device is again inthe position oi rest.

Adjusting of the time of welding The time of closure of the contactor b and, consequently, the time during which the welding current flows, may be varied by making the brush d2 (Figures 9 and l0) movable. When the brushes are side by side (Figure 10) the closing time of b is a maximum, while it is naught when the angular spacing of the brushes corresponds (Figure 9) to the angle occupied by the conducting part on the disc (Z. By making the contact di also movable, the point of the half-cycle may be selected where the welding current begins to flow.

' Embodiment according to Figure 11 In the embodiment according to Figure 11 the disc dcooperates with the contactor b for controlling the passage of the current in the welding machine. The purpose of this is to diminish the absolute error of time in the passage of the current by closing the primary circuit of the welding machine through a contact sliding on d, while avoiding any deterioration of said contact at the breaking point by effecting the breaking through the contactor.

The primary circuit is led through the massof disc d, a brush a and the main contactor b. Another brush d3 rests on disc d. It is shifted at a certain angle with respect to i in the direction opposite to the rotation oi the disc d. This angle is a function or the time constant of the contactor. The brush as is connected with the fixed contacts e2, at of a relay corresponding to the relays e-ei of the unit shown in Figure 8. I

This coil remains. Y

.small plates by spring blades. connection is through small plaited cables 39. (Another circuit 7,0 of the moving coil unit is Two cases are then possible. (1) The brush at is at this moment on a nonconducting partof disc d. Coil e is then nolonger energized, the contact is broken between el and c2 and established between e'l and 63. Consequently, as soon as the conducting part of it engages the brush d3, coil bi is energized and the contactor closes. However, the circuit of the welding machine is closed only when the conducting part of the disc it engages the brush -i.

For breaking, the non-conducting part of disc d engages first the brush d3. The energizing circuit of b is broken and the contactor opens before the insulating part of disc d'engages the brush i. Thus the current is already interrupted when ths sliding contact opens.

(2) If, at the moment of the depression of the pedal, the brush 113 is in contact with a conducting part of d: the relay e remains energized through el, e2, (13, d. Thus the circuit of b remains broken until :13 is engaged by the nonconducting part of d and so long as'it is not en= gaged by its conducting part. Then the'device operates as in the foregoing case.

Construction of the wattmeter by way of example in Figure 12.

The current winding I03 of this wattmeter is wound about a ring shaped magnetic core Mill split at 65. The slotted part of ring core 803'. projects through a window in the insulating plate 66.

The voltage circuit of the wattmeter comprises a metallic band 5i arranged edgewise in the air gap and forming a half-turn. The ends of said band are wound so that they lie flat in front of the small connecting plates 68 which are mounted on 66; They are connected with said The electrical made in the same manner as the voltage circuit 6?. It compensates for the fall of voltage in the electrodes. Figure 13 shows the connections of said circuit in series with a rheostat it. One

end of the same is connected with the corre- The above described moving coil unit engages.

at rest, screws such as 'H each extending through a transverse-piece such as 12 fixed on 66. It is provided on each side with an arm 13 which operates by means or an insulating finger it a scale contact such as 15. The contacts I5 are so arranged that only one or both are closed depending on the amplitude of the elongation of the moving coil unit. They act in the same manner as the contacts 2222' in the embodiment according to Figure 3.

I claim:

1. In an electric spot welding machine: a synchronous motor, a cam shaft with three cams driven by this motor, three control relays for controlling the welding circuit: a first relay for preparing the welding circuit, a second relay for" releasing the welding operation and a third relay for restoring the initial condition of the circuit, a contact in each of the relays controlled by the corresponding cam respectively.

2. In an electric spot welding machine: a synchronous motor, a cam shaft with three cams each of the relays controlled bysthe corresponding cam respectively, an electrovalve delivering the pressure for the application of the electrodes onto the sheetsto be welded, and electrical control.

means inserted between the electrovalve and the foregoing relays.

3. In an electric spot welding machine, the combination of a synchronous motor, a shaft actuated by said motor, three cams carried by said shaft, three relays tor controlling the welding circuit, said relays comprising a first relay for preparing the welding circuit, a second relay for discontinuing the welding and a thirdreley to restore the-circuit to its initial condition, a I contact carried by each of said relays and controlled by one of said cams, and contact means interposed between each relay and the adjacent relay, said me being controlled by the first to relay and controlling the adjacent relay.

DA sc i 

